"The main difference between these two devices is that the Ahmed implant has a valve mechanism designed to open between 8-10 mmHg, which serves to prevent hypotony and some related complications," Christakis explained. "The Baerveldt has no built-in flow restrictive mechanism, but achieves excellent long-term IOPs given that it has twice the filtration area of the mid-valve."

"The main clinical implications for the paper....is another set of data we can use to figure out what our next step of the procedure will be if [patients] fail," said Krishna S. Kishor, MD, of Bascom Palmer Eye Institute in Palm Beach Gardens, Fla., who was not involved with the study.

"In terms of preoperative extremely high IOPs, maybe you go with an Ahmed rather than with a Baerveldt," he told MedPage Today.

The trial included six clinics in the Canada and U.S., and one in Chile, and randomized 124 patients to the Ahmed-FP7 valve and 114 to the Baerveldt-350 implant.

Complete success was defined as an IOP of 5≤IOP≤18mmHg and ≥20% baseline reduction for all visits starting at 3 months with significant loss of vision or additional glaucoma procedures. Success was considered "qualified" if medications or surgical interventions were required, or if there was significant visual loss. Devastating complications or progression to no light perception (NLP) were considered failures.

Standardized surgical techniques were used. Baerveldt tubes were ligated with a releasable suture intraoperatively, and proximal fenestrations were made in patients with advanced glaucoma requiring an immediate IOP reduction.

The two patients groups were similar in ocular and baseline characteristics, with an average age of 66. More than half (68%) were white. Seventy percent were pseudophakic, 19% had rubeosis iridis, and within the glaucoma diagnoses, 50% were open-angle, 21% were neocascular, and 10% were uveitic.

There were five intraoperative complications in the Ahmed group, four vitrectomy, and one vitrectomy plus suprachoroidal hemorrhage drainage. There were four intraoperative complications in the Baerveldt group -- one vitrectomy, one vitrectomy plus iridectomy, and two choroidal detachment.

At baseline, the average IOP was 31.4 mmHg and most patients were on three glaucoma medications. At the follow-up 5-year visit, 72% of patients in both groups were present.

Failure rates were higher in the Ahmed group at 53% compared with 40% in the Baerveldt (P=0.037). The most common reason for failure was high IOP (>18 mmHg), which occurred in 89% of the Ahmed cases, and 65% of the Baerveldt cases, and additional glaucoma surgery, which occurred in 30% of Ahmed and 28% of Baerveldt cases.

The Baerveldt had a lower average IOP with an average of 13.6 ± 5.0 mmHg, compared with 16.6 ± 5.9 mmHg for Ahmed (P=0.004). These resulted in reductions of 57% and 47%, respectively. The Baerveldt group required fewer glaucoma medications at reductions of 61% and 44%, respectively (P=0.03).

Snellen acuity worsened in both groups from a median value of 20/100 at baseline to 20/200 at follow-up (P<0.001), but no overall difference in degree of vision worsening between the two groups appeared at follow-up (P=0.88).

Complication rates were 63% among patients in the Ahmed group, and 69% in the Baerveldt, however the Bleb Encapsulation was 11% in the Ahmed group and only 4% in the Baerveldt group.

Interventions were equal between groups at 51%, and most were slit lamp procedures, but paracentesis rates were 4% among Ahmed patients compared with 14% among Baerveldt patients.

"Most complications were transient and most of the interventions required were minor," Christakis said.

The researchers suggested that the device should be selected based on patient factors such target IOP, medication tolerance and goals of care, and surgeon factors (experience level, outcomes).

Christakis and co-authors disclosed no relevant relationships with industry.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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